Well, the fact that people aren't more comfortable sharing personal details sushi rollymously than pseudonymously on the internet demonstrates that sushi rollymity on imageboards isn't really a safety concern, unless the concern is other people finding out that you're posting on imageboards. That's the only reason anyone ever gives for not backing up their claims with some form of evidence, it would be recognizable.
Speaking of, projecting an identity onto someone is, logically, a perfectly valid way to deal with discussions on imageboards because nobody is able or willing to provide credentials which would map to credibility. I might not have a way to back up my claim of your identity, but you're not able to back up your claims either. Systematically, nothing gets to be credible if it's original.
Also, secondary communities are the norm outside of imageboards because other websites don't have group identity. Everyone uses most big websites, so the only reason you don't know that imageboard users do is because it isn't practical to tell others about your other exploits. People hate identity on imageboards, but being credited for what you make requires credentials. Just for wanting to share something the imageboards have grounds to call you names, because they perceive it as an attempt by you to establish identity for yourself while everyone else has submitted to their fate of being cattle camouflaged into each other. Yeah you're all equal. The point was making posting easy, though.